"Spending" the excess $500 contribution for 2019 in 2019 on does not resolve the excess contribution. You'll still have an excess contribution of $500 subject to a 6%, $30 excess contribution penalty each year until it is resolved. Since the excess contribution was made through your employer, the excess for 2019 would also be subject to taxation in 2019 and again in the year the excess is corrected if done by a regular distribution after the due date of your 2019 tax return. The penalty is not prorated.
Resolving the excess in some year after 2019 after the due date of your 2019 tax return would have to be done either by applying the $500 as part of your HSA contribution for that future year or, much less desirably, by making a taxable distribution that is also subject to a 20% early-distribution penalty if done before the age of 65. You could easily end up paying $240 or more in additional taxes and penalties if you choose not to obtain a return of the $500 excess contribution before the due date of your 2019 tax return.
