Only certain retailers offer 'Local Collect'. If the service isn't mentioned on their websites, you can't use it.
https://www.postoffice.co.uk/mail/collection-services
Amazon offer 'Local Collect' or 'Amazon Hub Counter' services at many Post Office branches. They also have 'Amazon Hub Lockers' at many locations (including railway stations, filling stations and supermarkets), where your parcel is left in a secure locker and you're provided with a code to open it.
https://www.amazon.co.uk/ulp/view
Some other vendors might use the services of couriers such as Evri (formerly Hermes) or Collect+, which offer the option to have parcels delivered to local stores. (Around here, most Co-op stores will accept parcels, both incoming and outgoing, for Evri).
However you'll need to check each retailer's website to see which delivery options they offer. There's no universal solution to your problem (unless, of course, you've got someone like a friendly neighbour who could help you out).