Its hard to open and shut are there bushings on the tailgate

THE LINKAGE MAY BE DISCONNECTED.

I've never even seen a Tacoma but usually these things work with thin steel rods inside the panel. Is the catch releasing on either side or not at all? If you can undo or prise off something to access the rod then hopefuly you can wriggle it enough to get the catch to release. Lashings of WD40 isn't going to hurt, just wipe it off the paintwork afterwards

You can try taking the handle out and fishing the rods up to the opening. Other than that, its a tough job.

by lock assembly i assume you mean at the handle... possibly the bushings for the lock arms are shot so the arms are off kilter or its just sticking, try some WD40 or something similiar on the sliding parts. spray and work it several times
also could be an alignment of the tailgate issue if the lock arms are binding

Your tailgate switch is bad or not adjusted properly.

Very easy, depending on how worn or corroded, you may need to spent a few minutes prying and wiggling the old one out, the new bushing will fit to place with some tapping, get yourself a block of wood and a hammer for insertion ( yes I said hammer and wood, this is the top dollar trick used at your local ford dealer)

unscrew the cover on the inside of the tailgate and you can inspect all the cables or connecting rods. also if it was forced shut just try pushing in on it hard and use the handle to open it cause the latch may be in a bind.

with the door open push the door switch and tailgate switch closed manually. if the warning stays on, replace the switch. if it stops, adjust the switch to make sure the door or tailgate pushes it down far enough.

under the carpet installed on the tailgate door, there is a hole. put a screw driver in it and manually flip the latch open, to start.
yjen take the door panel off, one screw with the interiro handle, and pull the rest off,
watch the auto release slidw side to side, you will find a broken piece here, I made an extension piece with a plastic hook and screw, works fine for over a year, lube all latch parts with wd 30 once opened.

Remove the inner pannel. Then move the handle the connecting rod from the handle to the lock will move.Then pull or push the connecting rod helping the handle. When you get it open move the handle again if it moves freely then most likely the catch needs adjusting to adjust loosen the screws aroung the catch on the rear pannel move the catch out a little try closing the tailgate if it takes undue force to close then repeat moving the catch out until it is easy to shut simple rule is if it is hard to close then it will be hard to open! Leave the inner pannel off until you can easily open the tailgate with the handle as you may have to give the handle a helping hand to open until you have finished adjusting.