If you google "Russian May Day Parade" you will obviously see this story, but the reference that shows up right away as the first wikipedia search plain sight on the top is the Victory Day Parade.
"Trump did not correct the reporter" is a silly discussion point.
The parade on May 1st pails in comparison to the one on May 9th. The May 1st parades are mostly people carrying banners and Putin is hardly out there making a big deal about it.
The May 9th parade is clearly the parade Trump is speaking about.
The whole verbatim tweet that you lifted from a reporter (and didn't credit the reporter) is silly gotcha journalism. It was some reporter thinking he was really smart and saying hey may day is a celebration of workers! Hahah trump doesn't know that!!! When in reality it just shows that the reporter didn't properly research that there is a military parade 8 days later that is state sponsored and celebrates the Nazi surrender. And they have tanks and guns and stuff and that they call May Day "Spring and Labour day".
This
article from the hill says it far better than the gotcha journalist you plagiarized did.
Also of note...