I need a fence for ERB239MSW sliding mitre saw

we do not sell anything on fixya.

Realign fence to blade, must be 90 degrees, using a level for straight edge bring other fence co planed with aligned fence. . You saw will only cut as accurate as you set it up., I spent over 2 hours on my 12 inch to ensure that it was vertical, exactly 90 degrees and exactly 45 degree both left and right. I used engineer squares.

Have you squared the fence to the blade/table. If the table is true to the blade, your mitre slot should also be. You can then squre your fence to the
slot

Few budget tools and especially generic, brand engineered tools imported from the far east are superbly accurate but tend to be "near enough".

You didn't say whether it is a hand operated mitre saw or a power saw.
Most power mitre saws have a number of stops that can be adjusted or filed in order to calibrate the angles and this process should be done when the saw arrives. Once both 45 degree angles have been calibrated accurately the angles in between should fall into place fairly well.

One problem with low cost mitre (chop) saws, even some so-called professional saws is the construction is so light, when pulling down the handle the machine flexes and spoils the cut. This is especially true when the handle is not set exactly in line with the blade or when not paying full attention when making a cut.

Having experienced such saws I have learned much about them so when I visit a tool store I examine their stock by twisting, rocking and pulling the saw heads and the amount of movement in many new saws of popular brands is disgusting, even some pretending to be premium brands. So far only a few of the most expensive types have impressed me.
That doesn't mean the others are unusable and with care fairly accurate cuts can be made when a suitable technique has been developed - like using a rifle with bent sights...

Have you checked on Ryobi? You might want to check Kreg fence. What type of blade are you using right now? I have a saw and I got online supplier for blades , I purchase on sawblade.com , happy with them. Good luck.

align blade and fence to mitre slot.

you need to remove the guide fence with the screws on the back. then you remove the throat plate and there is the bolt is that keeps it all together.

Just took one apart last week, not really difficult

move the blade until it is square to the fence then loosen the screws on the table with the degree increments and set to zero.

You will have to use a regular square to check out the crafstsman and find out where it is wrong.

You adjust the handle tension by actually adjusting the t-square itself, changing the relative position it sits from the rect tube mounted to the saw.
This is done by turning the two allen set screws mounted in the angle iron that is welded to the fence. There are a couple of tabs that ride along the inside face of the rect tube when the fence slides from side to side. You'll see that each of these tabs is adjustable, in or out, by slightly turning the allen set screws with an allen wrench. BOTH of these must be adjusted, so that you maintain the fence's 'squareness' to the table.
What I do is line up the edge of the fence with the mitre slot in the saw table, feeling the edge of the fence as it hangs over the edge of the mitre slot, both at the infeed and outfeed end of the slot. It should be perfectly flush at both ends.
By turning the set screws in or out a little, you can adjust the handle tension to the place where you like it (you don't need to force it into position to have it hold firmly; that's too tight). Then check the squareness of the fence by clamping it down along the edge of the mitre jig slot, and see if it's parrallel. If not, you need to adjust one or both screws to make it parrallel, and get the tension right. You may have to go back and forth a few times, but eventually you can dial it in to where it feels just right and the alignment is correct. Think small adjustments.
At the same time, put a little dab of wheel bearing grease or vaseline on the cam of the fence handle where it rubs against that little flap. This will make it easier to engage when the tension is firm and keep it from wearing abrasively.
This fence is a joy to use when it's dialed in. I hope you find this information helpful. Happy woodworking!