1.The auto-increment fields from database tables are made to generate unique ID each time a you record is added, and when one or more records are deleted the IDs used for deleted records cannot be reused for adding new records. But this is the normal behavior for these auto-increment fields.
2.In your case if you have deleted all records and you want to restart the identity from 1, the solution is to reseed its value to start from 1 like is indicated in the 1st solution above.
For more details about this you could read the next
MDSN link.[
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