Hi Yogesh,
To achieve this, follow these steps:-
1.Define aura:id of the child component in parent.
2.Define <aura:method> in child component and it will link to method of child controller.
3.Define a lightning:button on parent component and on click of this button get the reference of the child component as mentioned in step 1 and call aura:method as mentioned in step 2.
For further details you can take help from below link-
https://devops4solutions.com/calling-child-method-from-parent-component-in-lightning-components/#:~:targetText=Define%20aura%3Aid%20of%20the,as%20mentioned%20in%20step%202.
Thanks