As long as the previous employee did not tie their AppleID to this laptop, then you just need to perform a clean install of macOS. If it is an M-series Mac, then you can perform a DFU firmware Restore as well.
If they have their AppleID tied to the device, then they may still be able to control that device such as by erasing it & using the FindMy functions. If this is the case, then you will need to provide proof of purchase & ID of a person at the company authorized to act on the company's behalf to have Apple remove any system locks. You will need to contact Apple or an AASP to learn exactly what documentation & ID are needed & acceptable.
Here is an Apple article with instructions for re-purposing a Mac to another user....of course you can only begin at the erase step now:
What to do before you sell, give away, trade in, or recycle your Mac - Apple Support
I would highly recommend using some form of MDM management system in order to prevent a rogue employee from causing problems like this in the future. At the very least make sure a company AppleID is in control of the device so a personal AppleID cannot lock out the legal owner (aka the employer).