In Processes, it is possible to do a mass activation of archived forms. This will move the forms from archived status to the active status.    

Top Menu >> Processes >> Select process

Create a view to filter for your archived forms. This can be done using a custom view. Once the view has been created click on the More menu at the top. 

In the More menu, select Activate.

You will now receive a warning indicating how many archived forms that will be activated. Click Finish to activate the forms. 

If you try to activate more than 5000 forms at one time, you will receive a different warning indicating this limit. You are able to click Finish, and then run the activate again. 

Alternatively, clicking on Advanced will allow you to bypass this limit by disabling the webhooks. With the checkbox selected, click Finish to activate all the forms, 

 Further reading