I over contributed to my HSA in 2018 by $2875. This happened because I retired mid year and elected not to use COBRA to cover my wife. I am eligible to contribute $4450 to my HSA for 2019 and I haven't contributed anything yet. Is it possible to use the $2875 toward my $4450 instead of withdrawing it to correct the over contribution and separately contributing for 2019?
Yes, if you have an excess contribution in 2018 that you will not withdraw in early 2019, then you carry over that excess to 2019. This excess is applied as a "personal" contribution in 2019. This means that you need to make sure that you reduce your 2019 contributions so that the carry over plus your actual 2019 contributions are less than your annual HSA contribution limit.
You will be charged a 6% excise tax on the carryover amount next year.
If you withdraw the excess, it is still subject to regular income tax but not the 6% penalty. You need to make the withdrawal before April 15, and it will be a special procedure with the bank, not a normal withdrawal. Tell them you need to make a return of excess contributions. They will return the excess plus any interest it has earned, and you pay tax on the returned contribution and the interest.