Hello Heidy,
I would recommend following this recovery sequence to avoid losing any more formatting.
Create a backup: Close Word and make a copy of the affected document before making any changes. Keep the original unchanged.
Recover an earlier version: Check the shared drive, backup system, or File → Info for an earlier version of the document. If a previous version is available, compare it with the affected file and use it to recover the original formatting.
Restore custom styles: Open the document in Word desktop and check Home → Styles. If the styles are missing, use Word's Organizer to copy them from an older document or template that still contains them. Also check the Normal.dotm template for previously saved custom styles.
Restore margins: Go to Layout → Margins → Narrow and apply the setting to the whole document. If some pages still have different margins, check the section breaks and correct the affected sections individually.
Restore the custom bullets: Select the affected list and go to Home → Bullets → Define New Bullet. Recreate the bullet using the original symbol or restore the original graphic from a backup if it was an image-based bullet.
Save and verify: Save the repaired document under a new filename, close Word, reopen the file and check the styles, bullets, and margins. Compare it with the original layout to ensure the changes have been retained.
Prevent future issues: Once the document is restored, save a clean master copy and create a reusable Word template (.dotx) containing the approved styles and formatting. Store it on the business shared drive and maintain a separate backup.
Finally, check File → Account → About Word to record the installed Microsoft 365 version and build. Compare the update history with the date the issue first appeared and consult Microsoft's known-issues documentation. This will help determine whether the update is connected to the problem.
These steps should help recover the document systematically before making any further changes to Office settings.
Best regards