Unfortunately for you, you can't transfer funds between HSAs. But you do have a couple of options available, and how it's handled depends on whether you've already filed your 2018 tax return or not.
If you haven't filed yet for 2018, you will want to remove the excess contribution(s) before the filing deadline of October 15. You'll need to contact the bank or financial institution that manages your HSAs to request the change. Tax documents will be issued to reflect the withdrawal of excess contributions. If you wish to continue to have a separate HSA, you'll need to divide the max contribution by half for each calendar year, and deposit only that amount into each HSA.
I found an article that explains the process (and options) much better than I could if I went into detail here. The article is from 2016, but the procedures remain the same. I'm linking the article below. Hope it's helpful to you and will clear up how you need to proceed.
https://www.hsaedge.com/2016/11/06/how-to-remove-excess-contributions-to-an-hsa/
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***
