I still don't know what you're trying to accomplish.
FXi2 might be a SAP code and you're connecting to the APPL Application or the ABAP Object. If so See: https://www.sap-tcodes.org/tcode/fxi2.html
Here's what I think is happening... You're sending the command "fxi2" somewhere to something. That thing is replying "H" & ESC & "[0m".
"H" & ESC & "[0m" means "Hello, read you loud and clear. Over." 
Then you send to that thing above,the command "MBRMST", and it replies, ESC & "[0mMBRMST".
ESC & "[0mMBRMST" means, "Roger. Copy MBRMST. Over" 
Then you send a Tab character, and the thing replies, "_" & ESC & "[12;42H".
"_" & ESC & "[12;42H" means, "Aye, aye, Sir, will do. Over and Out" 
As you can see, there are two ways to learn what the appropriate Replies from that thing are. Find it's manual, or keep experimenting and keep a list of replies to commands, both the replies that indicate success and those that indicate an error on your part. What the reply actually means doesn't matter, all that matters to you as a Coder is success and failure.
Myself I would create a Module with a list of Mnemonic Constants for all the replies
Const fxi2_Ready As String = "H" & ESC & "[0m"
Const fxi2_MBRMST_Received As String = ESC & "[0mMBRMST"
Const fxi2_MBRMST_Tab_Received As String = "_" & ESC & "[12;42H"
That way, when you send an "fxi2", you know the reply should be fxi2_Ready
BTW, FXI2, (all Caps) is the SAP TCode for Change Report, according the the above link. If that link is relevant, you might want to use some more constants. Like
Const ChangeReport As String = "FXI2"
Const DisplayReport As String = "FXI3"
The purpose would be to make your code self documenting. The more your code reflects human reality, the better the code. At least IMHO.
Imagine
osCurrentScreen.SendKeys ChangeReport
osCurrentScreen.SendControlKey ControlKeyCode_Return
returnValue = osCurrentScreen.WaitForString3(ReadyTo_ChangeReport, _
NEVER_TIME_OUT, WaitForOption.WaitForOption_AllowKeystrokes)
Again, if that link is relevant, what your macro is doing is telling the Parent Application (SAP?) to Change Report, Report Type MBRMST. Or sumpin like dat.