Open the message you want to reply to or forward.
On the message header, tap the Reply icon or tap the Menu icon
, then
tap Reply all or Forward.
Add others to an ongoing conversation by replying to all and then adding the new person’s address(es) to the reply.
Tap the Send icon at the top right corner of the screen
to send your Gmail message.
You can change the message action after you've started the
message. Simply tap in the
message header next to the current message action and tap the one
you want. For example, if you chose Reply but decide you want to Reply
all instead.