Hi @mideruit ! Welcome to the forum!
When you check an older version of your app, your app will think that the database still is like it was in that time, but it’s not.
In your case it seems that you only added columns during the time, but it could be that columns or entire tables were deleted from your database.
So to prevent errors from trying to use a column that is not in the database, you should match both before continuing.
I think that 99,9% of the time you will match your app (that is, the files that tell your app the schema stored in your datatables) to the actual database. What this will cause is just a change of Settings that will create another branch starting from the old commit you checked out.
If you wish to continue further changes from that commit, you can normally. In that case I would recommend you merging with a more recent commit first.
If you do not wish, than you can ignore and continue your life normally back to your newest commit / branch.