How do I label a Simatic Panel HMI soft keys? I see no place to insert anything. It's like laser etched onto the soft key? The panel is a 6AV6642-0DC01-1AX1. It also has these numbers OP177B DP T/K-6 MSTN. I'm not a siemens person nor is my company and I need to replace this HMI on one piece of equipment with the new one I bought but it has no labels on the soft keys. 

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How do I label a Simatic Panel HMI soft keys? I see no place to insert anything. It's like laser etched onto the soft key? The panel is a 6AV6642-0DC01-1AX1. It also has these numbers OP177B DP T/K-6 MSTN. I'm not a siemens person nor is my company and I need to replace this HMI on one piece of equipment with the new one I bought but it has no labels on the soft keys. 

 Download the HMI manual. Then check paragraph 5.4 Labeling function keys on the TP 177B 4" and OP 177B

SIMATIC HMI HMI Device TP 177A, TP 177B, OP 177B (WinCC flexible)