OP, is that a local repair shop that you know & trust - or factory authorized service center under warranty, or post-warranty for replacement/upgrade or damaged hardware - most shops simply do a swap: pull, replace & restart if something failed. it also depends on whether your PC is a laptop/notebook usually with one HDD or a desktop with provisions for HDD#0 as well as optical/DVD and/or additional slots for SSD/HDD#1. Ask the repair tech. on their policies & guidelines on safeguarding customer's data - if you aren' sure, find someone else better qualified to do your repair.

If your PC was custom (re)configured with OS loaded on default HDD (C:\) and data & documents, etc. loaded on a 2nd. HDD/SDD, it's easy to take that out & just give them the rest of the system with OS drive on it - when it's returned to you upon completion, just have someone you know & trust to check & scan it.

If the repair needed is for OS related, including malware & virus removal, etc. - get a new HDD, partition it properly & do a fresh and clean install (or pay the shop for it, if you don't) and put the existing "old" drive in an external enclosure & recover it, then dispose of that after clean wiping it or as a spare afterward (to DoD spec. guidelines)