You want to edit or customize the alert text for an MTE node in RZ20
Go to RZ20 and click Open Alerts
MTE nodes which are red display alert texts that you wish to customize
In the Open Alerts view of RZ20, select the node for which you wish to edit the alert text and click 'Display alerts'
Highlight the alert and click the 'Choose Detail' button
Here you will see the Message ID of the alert text
You can then change this MsgID text in transaction SE91
You should try to keep the variables (like &1, &2, etc) in your alert text, because if you change the alert to some generic message text without variable symbols, then every alert will only report the same text without any details. The place holders &1, &2, &3 and &4 report the VAR 1, VAR 2, VAR 3 and VAR 4 field values in the alert text
Note that changing the text for this MsgID will of course change the alert text for all RZ20 MTE nodes that use this same MsgID
Translation can be done in SE91 with 'Goto -> Translation' in the menu
You can also change the Long text (ie. the F1 help documentation or Alert description for the alert in RZ20) in SE91 change mode by selecting the message, click the 'Long Text' button, and enter a custom Modification Name like "ZRT036"