I think this is what you need to consider. For me, it is very easy to manage these situations. However, this is because I have already struggled through many scenarios until I understood many possible solutions.
I can tell you that you will likely employ a DAO recordset to update one or more records that meet your criteria. However, you are skipping over important information contained in this thread. Before you can get to the point of updating records, you need to understand the dataset you will be working with.
I suggest you take a step back from your forms for a minute and try to create an SQL statement that simulates a test scenario. Consider a query that contains records you wish to update. Create this query via the Query Designer. Create a SELECT query. Add criteria to your SELECT query. Add something like
WHERE SFO_ID = 'SV498'
Then look at the SQL. Then ask yourself how this can be more dynamic. Maybe
WHERE SFO_ID = 'SV498' AND WHERE SFO_ID = 'SV499'
Work on the Criteria as the Criteria pertains to your business rules. Hardcode some criteria that creates a dataset you can work with. Develop a WHERE statement that retrieves the data you need, the records that will be updated. Then consider alternative ways to create that dataset. Then understand how one solution may be better than another solution. Then begin the next step, the step of implementation.