@Mariano welcome to the forum! So what have you tried so far?
If you create a small example flow that reproduces your issue and export it and paste it to a reply, it will make it easier for someone to help you.
In order to make code readable and usable it is necessary to surround your code with three backticks (also known as a left quote or backquote ```)
```
code goes here
```
You can edit and correct your post by clicking the pencil 
icon.
See this post for more details - How to share code or flow json
