Other answeres have pointed out the different possible meanings of sollen. But I would like to draw your attention to the fact that the past tense sollten, not sollen is used.
Should, be supposed to
Hacker im Auftrag Russlands sollten Trump zum Sieg verhelfen.
Probably really means that the Hackers were supposed to help Trump/ were instructed to help Trump. So here, I guess, "sollten" really has the meaning should. This connects with "im Auftrag Russlands", so it means that they were supposed to help Trump, because Russia ordered it.
Hacker im Auftrag Russlands sollen Trump zum Sieg verholfen haben.
If you change the time of the sentence, now the meaning of "sollen" is "allegedly". "Hacker ordered by Russia allegedly helped Trump to victory"
If "sollen" means "allegedly", it is mostly used as "sollen", not "sollten", because it is still not proven in the present.