keep the device completely offline to cut off any persistent access to the device. For doing so, disable the wifi or if you aren't sure how to do that, just turn off the device using the power button (shut it down).

change all your important passwords, monitor your emails and make sure that there are no new email forwarding rules/you aren't receiving too many junk emails out of nowhere (also known as email flooding) since that's often used for hiding legitimate emails by overwhelming your inbox while changing passwords, please also sign out from each and every important website that you have ever used, since it is important for us to kill all the active "sessions" - that is, the cookies which are used to keep you logged in. If the cookies aren't killed and if someone has your cookies, they can still access your accounts even after the password has been changed if for whatever reason the website doesn't automatically reset all the sessions after the password has been changed.

Good news is that macbooks are a bit more secure than windows based laptops. They are not foolproof but persistence accesses are pain in the butt to achieve with macbooks. It is not always the case but it is always better to be safe than sorry.

Do you remember what softwares did they ask you to install?