When validation errors have been corrected, for example mappings have been made, it is possible to re-validate the publication.
Click the three dotted icon on the row for that publication and select "Validate" in the pop-up menu.
The current number of validation errors will be shown in the pop-up window.
Click "Validate".
More information:
Step by step guide from uploading to publishing master data.
How to see that a publication has been validated with errors?
How to see that a publication has been validated with no errors?