Hello @SmritiFotedar,
The Update data activity generate variables with update and insert counts, you can use them on your alert by calling them like this :
<%=vars.insertCount%>
<%=vars.updateCount%>
For the reject count, you can activate the reject outbound transition on the Update data activity, add a js after to affect the reject recCount to an instance variable, and the use it in your alert like this :
<%=instance.vars.rejectCount%>
Br,
Amine