So after copying some files to a 7z file the archive turned into a .tmp file. Should I do something about it or should I leave it that way?

I mean it still works like an ordinary 7z file. Should I rename it to .7z? Is it safe to do that?

Edit: now it's a .7z.tmp file

Edit: Ok so I checked Event Viewer and there was indeed an error:

Log Name:      Application
Source:        Application Error
Date:          16/04/2019 23:45:46
Event ID:      1000
Task Category: (100)
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      LAPTOP-HJTN59RN
Description:
Faulting application name: 7zFM.exe, version: 18.5.0.0, time stamp: 0x5ae70540
Faulting module name: 7z.dll, version: 18.5.0.0, time stamp: 0x5ae70540
Exception code: 0xc000041d
Fault offset: 0x0000000000069748
Faulting process id: 0x2ffc
Faulting application start time: 0x01d4f49a1b526494
Faulting application path: C:\Program Files\7-Zip\7zFM.exe
Faulting module path: C:\Program Files\7-Zip\7z.dll
Report Id: 20cb20fb-9d0f-472d-ad9c-52dc9c35723d 
Faulting package full name: 
Faulting package-relative application ID: 

If you are certain the file is working OK, I don't think there is any issue renaming the file removing the .tmp portion of the file name.

As I noted in my comment, 7zip creates the .tmp file while it's working on a process, and typically removes this file once the work is complete. You may wish to check your 7zip settings, check the Event Viewer and any logs 7zip creates to see if there was an issue you need to be aware of, but, so long as the file IS working, renaming it should be just fine.