If it doesn't have a small screw, then look for a small indent that you can put a small screw driver to open it up where you will see the battery.
I need to do step by step the process to program my garage opener door from my 2003 Lexus model# sc430
In the black box drivers side fender, of course under the hood.
90,000 miles
225.00 a corner.
Panasonic CR 1616
y
The battery is located under the bench seat in the back seat. I know because I have a 2003 Bonneville.
3 button fob 2003 onwards cr1616
remove seat, remove neg cable from frame and Pos from battery, remove strap and take out battery.
If that's dollars it is.
You have to take the front passenger tire off and a plate under the wheel well to get to the battery.
Take both cables off. Remove old battery. Put new battery in. Put cables back on.