How do you write a seven thousand dollar check?

The same way you'd write a seven dollar check, except you need more zeroes in the amount box and you need to include the Word "thousand" on the line where you write out the amount in Words.

Most banks don't place any limits on personal checks (provided that the account they're drawn on has the funds to cover it), and even if yours does, it's doubtful they'd balk at a piddling seven thousand dollars.

If you have a long history with your bank and you've never written a check for more than $100 before, it's possible your bank's fraud detection systems may trigger an alert if a $7000 check suddenly comes in. But that doesn't have anything to do with writing the check a special way (in fact, if you do write it a "special way", that will probably be taken as even more evidence you didn't actually write it).