Have you considered contacting the council to ask for help with a rat infestation and mentioning that you’re near a restaurant that appears to poor rubbish handling practices.
This will give them several opportunities to investigate the source, including whether or not the restaurant also has rats inside.
If you’re in a mixed residential/commercial building then the residential OC may have to talk to the commercial OC to get them to deal with the restaurant and its alleged poor cleaning practices.
Or would you feel confident to approach the restaurant directly and mentioning that there are rats and you’re wondering if their rubbish handling practices are causing the problem. Also, tell them that your tenant has had damaged caused by the rats and you’re considering going to council to get them to investigate.
It might just frighten them into acting responsibly.
Of course in the midst of the current COVID-19 pandemic, it might be the straw that breaks the camel’s back and cause them to close leaving you with nowhere to seek restitution for the damage caused.