You'd start with what I'd call your development FE - the one that you kept to yourself as the basis upon which all new development was derived from when you issued updates. Re-link the tables in it and distribute copies of that as your new front end. If this fe is 2007 and you now have 2016 on your pc, AFAIK, it will attempt to save your 2007 version as 2016, which should be OK as long as no backwards incompatible features are involved. While it could be said that since nothing was changed that was only available in 2016 so it should be OK, problems can arise from insidious features that you may not be aware of. Database sort order is just one, perhaps. So I would only re-link as described, using the later version of Access, on a copy of your development file. Then see if users with 2007 can open it.
If anyone is missing RunTime, the solution is obvious - they need it or a full working version.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.