Button gear selector will not push in so I can go from park to reverse

Can park be selected by going under the vehicle and manually pushing the gear selector into the park position?
If so then cable adjustment is next.

key wont come out or turn to off until gear selector is in park [ recognize that its in park ] your selector or transmission selector cable is damaged

What make , model , year an engine size ? All vehicles have a safety system ,shifter interlock . This system will not let the gear selector move from park unless the driver is pushing the brake pedal . Has a electrically controlled solenoid that locks it in park , also has brake pedal switch . Could have a control module involved ,like a BCM - body control module etc.... Maybe he broke the gear selector cable or a plastic part on the end of the cable. Looking under the hood at the transmission connection of the cable while someone moves the gear selector ,does the transmission selector move .

have your gear selector /linkages checked

Transmission may now be toast since you continued to drive it when maybe low on fluid or torque converter had failed. How long since last fluid and filter change? Ever?

Make sure your brake lights are working, the shift interlock may not be getting signal from the brake light switch to release the shift lever. If they are working, the problem may be the shift interlock switch.

Check your linkage bushing. Those tend to break, very cheap fix, Dorman makes a replacement.

Could be the brake switch or the solenoid that locks the shifter in park.
That circuit would need to be tested.

you car likely thinks its stuck in reverse, which it may be... even if you can roll it. you'll need to find a way to either get it into park or neutral, normally this can be done by the actual linkages under the shift console or from underneath the car.

ALWAYS engage the Parking Brake BEFORE putting car into "Park". When you want to get out of "Park", put your foot on the brake pedal, move gear shifter into desired gear, THEN take down Parking Brake. If you get stuck (gear shifter doesn't move), then try the "rocking" method (recruit 1 or 2 folks to push your car from behind while you try to move gear shifter into desired gear). Good luck!