Most vehicle manufactures recommend changing your transmission fluid and transmission filter at least every 100,000 to 150,000 miles.
But if you can change the transmission filter and transmission fluid around 50,000 to 70,000 miles that would be much better as it will protect your transmission and prevent breakdowns.
Changing the transmission fluid and transmission filter is cheaper than replacing or rebuilding the transmission when it fails due to bad fluid and a clogged transmission filter.
Always change the transmission fluid and transmission filter at least every 150,000 miles to protect the transmission from failure and damage.