If you have at least $866 of medical expenses in 2018, and don't make further withdrawals, then that will take care of the issue.
Also, I didn't notice that you are spanning two years. If your expenses were in 2017 and you already filed your 2017 tax return and claimed the expenses, but the HSA withdrawal was in 2018, then the withdrawal is not a taxable recovery on your 2017 return at all. It would be a taxable recovery on your 2018 return, if it is a recovery at all.
So you really have several options.
The least good option is filing an amended 2017 return to reduce your medical expense deduction by $2000. Amended returns just make too much work for everyone. But if you did that, you could ignore the HSA withdrawal and continue to withdraw money in 2018 for new expenses without worrying about it.
One good option would be to send $866 back to the HSA bank now, as a "return of mistaken distribution." That way, you don't have to worry about any future expenses. You can withdraw for 2018 expenses or not, without having to keep track. Not all HSAs will accept a return of mistaken distribution, and this is a special form and procedure, not a regular deposit.
The other pretty good option is to keep the money and wait and see what happens for the rest of 2018. For example, if you had $500 of expenses and don't take any more withdrawals, then you would have a taxable recovery of $366 to report next year.
The IRS has no way of knowing, other than random audits, that you used the 2018 HSA money for a 2017 expense that you also deducted, instead of for a 2018 expense. If you ignore the issue, you have a decent chance of getting away with it. That doesn't make it right, and if you do get audited, you can face penalties and interest on the back taxes.
