Hi @paramitakundu,
Welcome to the Solace Community! Currently the Cloud Stream Binder for Solace does not support manual ACKs, however there is an enhancement open that you can follow and a little birdie told me it should be supported in the next major release of solace-spring-cloud 
Right now my best guess is that release will be in the November time frame but I’ll try to remember to update this thread when I know more.
I know it’s not as useful as doing a manual ACK, but keep in mind that the pubsub+ cloud stream binder will automatically ACK your message after the app returns successfully. If your app throws an exception the message will be requeued.
-Marc