Viens is the 2nd person singular imperative present of the verb venir: to come.
I would not put a hyphen in “Viens là”, I can’t see any reason to do so. Viens et là are two well separated words, as in “Come here”.
As a french, the “là” comes with an hyphen in “Viens-là” or when it follows a verb or a noun.
Although the rules governing the French hyphenation may be confusing sometimes there is not viens-là. It is viens là sans hyphen.
You can learn more for the french imperative here
The verb and the pronoun are linked together with a hyphen in the affirmative imperative.
Excusez-moi. (Excuse me.) Aide-nous. (Help us.)
There are cases when both direct and indirect object pronouns are present. During these scenarios, the DIRECT OBJECT PRONOUNS always come BEFORE the INDIRECT OBJECT PRONOUNS.
Donnez-la-nous! (Give it to us!) Prête-les moi! (Lend them to me!)
But là is but an adverb like here, there and the like. No need for hyphens. There are indeed some webpages using viens-là but this is not correct french. It is just (I guess) for help the users to memorize the link and for https convenience:-)!