You can just rename .blend1 files to .blend and work with them in Blender normally. This is because .blend(number) files are just backups done automatically so users can revert the changes and do not lose the data in each step. It appears that this backup function was in Blender as far as 2003 and maybe earlier.
Convert Blender backup file to Blender 3D data file.
We found 3 software records in the database related to .blend1 to .blend file format conversion.
Microsoft Windows software - convert blend1 to blend on Windows
A very popular free program used for work with 3D graphics
Convert from blend1 file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned blend1 to blend. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Apple macOS / Mac OS X software - convert blend1 to blend on OS X
The Mac version of popular free 3D graphics software
Linux/Unix software - convert blend1 to blend on Linux
Easy-to-use 3D modeling utility