@Andrea-Salvemini, you're right - you can't link two IFTTT accounts to the same TRIGGERcmd account. If you link a second account, the first account becomes un-linked.
You don't need IFTTT though.
I assume you're trying to use the original TRIGGERcmd Alexa skill which does not work with Alexa routines.
The Smart Home TRIGGERcmd Alexa skill does work with routines. It simulates an Alexa Smart Home on/off switch for each of your commands, so it works with routines. You can flip the virtual switch by saying, "Alexa, turn on calculator" but you can also say whatever you want if you use a routine that flips the Smart Home switch.