Hey @Jenny26 you should be able to do this through the new association actions beta in workflows. If you go to the section to opt your account into betas, then find the beta for “New Workflow Actions for Associations” you can enroll.
You’ll need a common property value across all the deals, which if you don’t have already you can set through workflows too. “Company domain name” would be a good one to use as it’s unique to each company record, if you create a deal workflow to copy the company domain name from a company into a custom deal property it will give all your deals a matching property value, then you can use the associations action to associate all deals with a matching company name to each other, something like this:
