There is no direct "lot split" button in standard Odoo, but you can achieve this using Physical Inventory (Inventory Adjustment). Here's the step-by-step:

Go to Inventory → Operations → Physical Inventory and create a new adjustment. For your product, add three lines: first, set Lot 001 → quantity to 0 (to clear the original lot), then add a new line for the same product with Lot 002 → quantity 5, and another line with Lot 003 → quantity 5. Validate the adjustment and Odoo will restructure the stock accordingly.

So use this approach when traceability is not a strict requirement and you simply need to restructure lot quantities. If full traceability is needed, a custom development or a third-party OCA module for lot splitting would be the right path.