When you click other, there will be a drop down list for grandchild. You do not need to amend, if that is the only change. A grandchild is considered closely related.
It is not necessary for a taxpayer to have provided all the child's support to claim the child. The most important thing is where the child lived.
FULL RULES
A child closely related to a taxpayer can be a “Qualifying Child (QC)”
dependent, regardless of the
child's income, if:
1.
He is under age 19, or under 24 if a full time
student for at least 5 months of the year, or
is totally & permanently disabled
2.
He did not provide more than 1/2 his own
support
3.
He lived with the relative (including temporary
absences) for more than half the year
4.
He is younger than the relative (not applicable
for a disabled child)
5.
If the
child meets the rules to be a qualifying child of more than one person, you
must be the person entitled to claim the child as a qualifying child (this
essentially means that you have the parent’s permission to claim the child, if the child also lived with the parent more than
half the year)
6.
If the parents of a
child can claim the child as a qualifying child but no parent so claims the
child, no one else can claim the child as a qualifying child unless that
person's adjusted gross income (AGI) is higher than the highest AGI of any of
the child's parents who can claim the child.
https://turbotax.intuit.com/tax-tools/tax-tips/Family/Rules-for-Claiming-a-Dependent-on-Your-Tax-Ret...
