How to I reserve an appointment for store technician?

You simply call the local number for your Apple retail store and ask for a time. I've found their system easy to use.

You can also make a reservation online:

https://expresslane.apple.com/GetSASO?PRKEYS=PF2&locale=en_US

HOWEVER, Apple no longer works on PowerBooks. They will tell you to contact an independent Apple Authorized Service Provider or other reapir source. I have a 2003 PowerBook for which I'd ordered a new battery and charger. When I had a question on the new charger I took it to an Apple Store for evaluation---this was about 2010-2011. The tech told me it was good I was asking about the newly-bought charger because he was not allowed to work on the PowerBook itself because it was well past their service cutoff. The cutoff seems to be about five years.

What is your problem?

 Cheers, Tom 😉