Delete All Records
#for all records
db.session.query(Model).delete()
db.session.commit()
Deleted Single Row
here DB is the object Flask-SQLAlchemy class. It will delete all records from it and if you want to delete specific records then try filter clause in the query.
ex.
#for specific value
db.session.query(Model).filter(Model.id==123).delete()
db.session.commit()
Delete Single Record by Object
record_obj = db.session.query(Model).filter(Model.id==123).first()
db.session.delete(record_obj)
db.session.commit()
https://flask-sqlalchemy.palletsprojects.com/en/2.x/queries/#deleting-records