How to boost my Experian score ?

My TransUnion score is 670, equifax 600 and Experian 636 .

I moved here to the ‘US since march and got my social security number in may . I signed up for kikoff credit building 3 months ago and it seems like my TransUnion is getting boosted more by few point . When i got my socials , my score was 630 by default but my TransUnion has been adding more scores than my Experian and equifax.

I was told to get a secure credit card because that will help me boost it up .

What credit is advisable for someone in my score range ? I was thinking of getting a car on finance but the APR i got was around 27%