Union different dataset in Fuseki

[Glenn TheMan]

Hi, I am trying to merge two models (with some redundant info) that are persist 
in two different dataset's in Fuseki (3.14). I am using the included SPARQL 
query console and set the endpoint for the query to 
http://localhost:8080/fuseki/.
How would the SPARQL syntax look like to merge the similar datasets (using 
select, construct or optional)?

Greetings.

This is my attempt;
PREFIX a: <http://localhost:8080/fuseki/model1/>
PREFIX b: <http://localhost:8080/fuseki/model2/>
SELECT ?s ?p ?o
WHERE
{
  {
    ?s  ?p ?o
  }
  UNION
  {
    ?s ?p ?p
  }
}