Firstly, you will need to empty the subsite-specific recycle bin.

1. Navigate to the subsite you want to delete.

2. On the ribbon bar, click on Site Contents.

3. Under Site Collection Administration, select Recycle Bin.

4. Select the subsite’s recycle bin and empty the items.

5. Click on OK to confirm the deletion.

Once the subsite-specific recycle bin is empty, you can delete the subsite.