Bulk update site definition

Hi,

I'have migrated a wiki library from my Onprem SP 2013 to SP Online.

After the migration I noticed that most of the pages were plain white pages.

I then launched SharePoint designer and noticed a small "!" symbol. After reapplying the site definition, my pages were visible again.

Is there a way to automate the "Apply site definition" in bulk mode, either with a tool or with Powershell ?

Thanks.

R.