Assuming it's a 3-position combination, try:
50 - 25 - 50
50 - 0 - 50
25 - 50 - 25
25 - 0 - 25
The first one is the "standard" default combination (don't ask), the other three are just in case the manufacturer uses something else.
If you DO get it open, change the combination to something else IMMEDIATELY. And stay away from the last digit of the numbers with a 0 or a 5 (makes it easier to guess). Recommend using a 6-character word, with no relation to the contents or the line of business.
And depending on what you're storing, you'll want an absolute minimum number of people knowing the new combo. And if you do write it down, make sure it's stored in a secure location (which isn't your wallet).