That's not going to be easy : not that Suevians didn't managed to get half of Spain in their time, but Rome had still enough teeth to bite their hand, and Goths were precious allies there.
Too great of an expension, too soon, and Suevians would be crushed as IOTL and giving their excentric center in Spain, wouldn't really be able to dominate whoever controls the center or the east of the peninsula.
Having Rechila dying quickly, or being deposed, after having captured Merida and limitating Suevian control (that was thin IOTL in these regions) would probably help not making Suevians as "prime targets".
Basically, let Goths blown their own trumpet, in Gaul and in Spain, and serve as main antagonizers ITTL.
Then Suevians could, if Rome still fall (or decline hard enough to loose grasp on most of Spain) resume their expansion in Spain, Frankish-style (especially if they convert to Nicean Christianism ITTL, as they did quickly and superficially IOTL before turning to Homeism).