The Brown Bear has a +5 to hit in its stat block (see
https://open5e.com/monsters/miscellaneous-creatures/brown-bear.html).
However, you and your DM are free to interpret the vague wild shape rules any way you want. To facilitate this, my sheet offers several ways to have the wild shape stat blocks calculated. You can select the calculation way from the "Wild Shape Options" button on the top of any wild shape page. In the FAQ you can find an explanation of how the different methods work.
In the case of the Brown Bear, something else is afoot. Because the monster manual calculates its attacks as Str (+4) plus proficiency bonus (+2) plus an arbitrary penalty (-1) the sheet will always put a -1 on the attack, because that is what the monster manual suggests should be added to the attacks of a Brown Bear.
You are still free to change the to hit to anything you want, but I suggest talking to your DM about how to interpret this.
