Hey mchristina144,
If you've forgotten the login password for your old MacBook Pro, there are a couple of options you can try to get back into it.
Using Apple ID:
If you’ve set up your MacBook to use an Apple ID, the login screen should eventually prompt you to reset the password that way. Apple has a guide on this posted here: If you forgot your Mac login password - Apple Support.
If Apple ID is Not an Option:
You can also reset the password by booting into Recovery Mode . You'll need to restart the Mac and press Command + R as it turns on. From there, you can use the recovery utility to reset the password. Apple has a detailed guide on this process here: If you can't reset your Mac login password - Apple Support.
If you’re not sure which route is easier for you, start with the Apple ID option. Best of luck to you.