I'm not sure that I understand your set up. Here's my best guess:
You are selecting values from a drop down list. The drop down list is set to list values from the same field as the one set up with the drop down list which enables users to automatically add new values to the drop down list simply by typing a new entry in this drop down list field.
Is that correct?
If so, you can do the following:
Enter find mode
Select a misspelled entry from the drop down list.
Perform the find
If a single record is found just edit the field to correct the misspelling and it will disappear from your drop down list.
If multiple records are found, you can edit the field in your current record and then use Replace Field Contents to update the other found records with the same value.
Repeat until no more misspelled entries exist in your list.
But I am making a lot of assumptions about the design of your database that may be incorrect.