To merge two talent pools, you will transfer the one with fewer candidates into the second pool. You can then delete the first pool and rename the one you wish to keep if necessary.
To perform this action, go to the Admin/Pools (Viviers) menu, then click on the number of Candidates next to the name of one of the pools you want to merge.
You must then select all the candidates in the pool and click on the green button "Place in a pool" to assign them to the other pool to be merged.
Warning: The selection will only include candidates from the current page; it may be necessary to go to the next result page and repeat the same action. Once all candidates are in the final pool, you only need to delete the first one.
If your pools contain many candidates, it may be preferable to first increase the "Number of rows displayed per page in listings" in the My Account menu (you can lower this number afterward if you do not need it, as pages load faster with a lower number).