in vim, after renaming the file, swap file exists, it is a pity to delete old swap file

Question

After renaming the edited file and after recovery is ok, vim gives the recommendation to delete the old swap file.

That can easily be done. And all works fine. But it is a pity to do so.

The old swap file is 163840 Byles long. The new swap file has only 16384 Bytes.

There are valuable data in the old swap file from the forgoing long editing process. These are going lost when deleting the old swap file.

I would like to incorporate the data from the old swap file into the new swap file.

The documentation to swap file is very sparse.

Do someone know how to accomplish this?