That's not good. Booting into recovery mode like this might mean just that you have some data which are incompatible with the new software, but it may also mean that the update wasn't installed correctly.
The first thing I'd try is erasing the cache. Unfortunately someone (probably Samsung) has tried to make this "friendly" by introducing non-standard wording: I can't see a "clear cache" option, and don't know what "erase app data" means: it might be a silly way of saying "clear cache", but it could clear more than that. I cannot see what option is highlighted in the picture as it's unreadable.
So, suggestions:
1) Remove the SD card, just to be safe.
2) Can you boot into safe mode? If you can then the ROM is fine and this is just a data problem (so back up, then be ready to clear cache or factory reset - the latter should certainly do it, but any data not backed up will be lost).
3) If you can't, then do what it says on the recovery screen: try the "erase app data" option (unless perchance the unreadable highlighted option is to clear cache/temporary files, in which case try that). Then see if it will boot normally.
4) If it won't, see whether it will boot into safe mode. If you can it's a data problem.
5) If it still won't, your options are either:
a) Try a factory reset (may not fix it, will lose any data not backed up. This is why I suggested removing the SD at the start, to be safe)
b) Go to Sammobile.com, find the latest firmware for your exact model (not just "S8", but model/region/carrier), download that and try flashing it. You'll need a computer and some Samsung software - I think these days you may use Smart Switch rather than Odin, but there will be instructions on the site. This may or may not factory reset your phone in the process (I don't know for Samsung, but for many manufacturers the equivalent process does a reset).
c) Take it back to the shop and ask them to fix it, or contact Samsung and tell them that their update failed and the phone will not boot (and that you've already done the other things it says on the recovery screen - otherwise the call centre's script will tell you to do them first).