Let it go without adding any yeast. Yes, you probably lost a bit of yeast out your blowoff tube, but you obviously have plenty left. All that krausen filling the head space in your fermenter is filled with yeast. Wait until all of that has fallen and the surface is clear. Until then the yeast are still working. Once they all fall to the bottom of the beer they are finished. Then you can check gravity a couple of times to be sure before packaging.