Selecting Existing Data to fill in for old dates

Please forgive me if this isn’t the right place to post this, I am pretty new to Influx and am not a DB guy at all (as I am sadly learning).
I am looking for a way to generate a search for a current block of time, and use that to fill in old data. The short of it is I am missing about 4 days of metrics, and want to take a sample from the previous four days to fill in the missing data. It’s a number of metrics such as memory % used, CPU load (5 min) and a few others. I have been knocking my head all day trying to get a query to work with the HTTP API, or CLI, to no luck, and not in a way I can easily update the results to plug them back in for a different date. If anyone can point me to a method or something that will help I’d really appreciate it, a nudge in any direction would be most helpful after a day of frustration.
Thanks in advance,