A change of mind
Definition 1 of 1
Pro Tip 1/3Decision Reversal
Indicates someone has reversed their original decision or position on an issue. 
She initially refused the job offer, but after a change of mind, she accepted it.
Pro Tip 2/3Not Negative
Changing one's mind is a normal part of human thought process and not inherently negative. 
Even though he had a change of mind about moving, everyone supported his new decision.
Pro Tip 3/3Moment of Doubt
Can imply a moment of doubt or reconsideration before making a final decision. 
After a change of mind, she double-checked the contract before signing it.