It’s really easy, because there are many free plugins for this.
If you want to add custom tab per each product, use Custom Tabs plugin
If you want to add global custom tab for all products – use our RH Woo tool plugin, download it from Rehub – plugins section
After installing, go to Woocommerce – settings – Rehub Tools. You will see there 3 fields for tabs
In names, add names for tabs. Divide with semicolons.
In Contents – add content of tabs. Divide them by word EOT;
and in Orders – add priority. Default priority of woocommerce tab is 10.
Of course, it’s very important to have the same number of custom tabs in each field