How do you change stock basis (Line 1) and loan balance at beginning of year (line16) on Form 7203?

to get to it (after entering the k-1) in the search box type 7203. iit may not be required. however, the IRS recommends it so constant track of your basis is maintained. 

iRS instructions

Who Must File
Form 7203 is filed by S corporation
shareholders who:
• Are claiming a deduction for their
share of an aggregate loss from an S
corporation (including an aggregate
loss not allowed last year because of
basis limitations),
• Received a non-dividend
distribution from an S corporation,
• Disposed of stock in an S
corporation (whether or not gain is
recognized), or
• Received a loan repayment from an
S corporation.
It may be beneficial for
shareholders to complete and
retain Form 7203 even for
years it is not required to be filed, as
this will ensure their bases are
consistently maintained year after
year.