Jean Anne Mayhall:
Thank you for your post.
After entering a check mark in the first record, pull down the Records menu and select "Replace Field Contents...". A "Replace Field Contents" dialog box will appear saying "Permanently replace the contents of the field <field name> in the <x> records of the current found set?". The first option below "Replace with: <value>" will be selected as a default. If you then click "Replace" at the bottom, all records in the found set will be set to that value.
If you find a subset of records, it will replace only those subset. If all records are displayed, it will replace all records with that value.
Let me know if you need additional clarification.