I'm us.ing a tablet...can reach and use one gmail address but not my second one

It begs the question what message do you get when you try to connect to the second one. Speculating, mail might be temporarily stuck in a server somewhere. Or, that account was locked because someone (maybe you) tried to access it from another device from a location that tripped a security precaution. Or, maybe you are mistyping the password for the 2nd account. Have you tried the "forgot my password" on the second account? If you can get into the second account, here is something you might consider:

https://business.tutsplus.com/tutorials/how-to-combine-all-your-email-accounts-into-one-gmail-account--cms-21305

If you click on your icon top right, you should be able to access an option to sign in as other user, which would in this instance be your other account. Of course, you would have to enter in the sign in details for that other account. Hopefully, you have recorded both of your email addresses and both of your passwords in a password safe. You need to be sure that you are entering the second account with the correct email address and password.