To address this problem, copy only the necessary fields in the spreadsheet for CRM creation or update, and paste them into a new spreadsheet. Try re-importing the document afterwards.
If this fails, a CRM admin user would need to increase the attachment size limit by following the below operation steps.
Log in to CRM as an Admin user
Click the Profile icon and select Admin
Click System Settings
Under the Advanced grouping box, update the Maximum upload size value as required.
Click Save
