97 bravada

I am having an issue with my transmission won't go in reverse but will go forward please it's our only car aND am really hoping to not have to replace transmissiin

Bad news here , this is always internal if the linkage is working properly.

Sounds like a shift solenoid issue.
It very important to either have your Bravada towed to a trans shop on a rollback or take a chance driving it, shifting your gears manually. I'd go with the rollback wrecker to avoid damaging your transmission. My wife drove it with bad solenoids and the bill was over $1200.

How do you change shift linkage are there any special trick to installing

I believe Maxwedge is referring to the shift linkage adjustment.
If the car doesn't move with the gear selector in Park and the shifter lines up with each gear you feel the "notches" as you pull the shifter, the linkage is likely in proper adjustment.

I believe there is a trouble code for transmission issues but it takes a code reader that can read transmission codes.

If you have all forward gears, it is not a shift solenoid problem.....unfortunately, when you have no reverse, if you drop the pan, you generally find metal in it, meaning an internal problem....

Can easily check linkage....with e-brake applied, just shift to reverse....if you have backup lights on, it's ok....

Have you checked transmission fluid level and condition? Scanned for codes?