For the synchronization of your steps between Gymlib and Google Fit to work correctly, use the Google account linked to your Google Fit account. To verify or change your Google account:
Go to your Google Fit app;
See which of your Google accounts are being used;
Click on “Profile”, “Settings” then go to “Manage connected applications”;
Check that Gymlib is in the list of connected applications, via the same account used for Google Fit. If this is not the case, click on “Gymlib”, then on “Unlink” then add the correct account;
Return to Gymlib to link the correct Google account.