Power washed and waited for beams to dry, applied cedar tint stain , now have some dark spots on the cedar beams . How do I remove spots and reseal?

No easily. Apply a second coat and see if it blends them in. Otherwise, you can strip it back to bare wood and restain but that's no guarantee it will not happen again. Cedar and redwood are known for spotting due to the oils in them.

My feeling is that if you didn't seal the cedar when new, you are out of luck.