Hi Luis and welcome to the Community!
While there is no “UPSERT” action in EasyMorph, the canonical way of doing upserts is to derive two tables, and then use the “Keep/remove matching” action to keep records that already exist (and need to be updated) in one derived table, and new records (that need to be inserted) in the other derived table. Then use the “Update” action in one derived table, and “Export to database” in the other.
Also, to check whether a record ID exists in Snowflake, you can use the “Select matching DB rows” action.