The "reserved stock" type in Inventory Logs is merely informative (for your own records) but it doesn't "reserve" it in any way. So, if you use the "Reduce Stock" button, it'll reduce that amount from the available stock as it happened.
But, later, If you want to re-add the same stock again, you just have to use the "Increase Stock" button.
Alternatively, if you want to have the stocks separated ("main stock" and "reserved stock"), you can create multiple inventories for any product with our Multi-Inventory add-on. And creating one for the main stock and another for the reserved stock.