In the vast majority of cases, you double their lift/push/drag/carrying capacity
Size and Strength. Larger creatures can bear more weight, whereas Tiny creatures can carry less. For each size category above Medium, double the creature's carrying capacity and the amount it can push, drag, or lift. For a Tiny creature, halve these weights.
—Lifting and Carrying, Player's Handbook, pg. 176
There's a few generalizations we can make based on this rule:
- There's no difference between Small and Medium creatures; they both use a multiplier of 1x.
- There are no [Officially Published] Racial Options in 5e that are 'Small'-sized, and have this feature
Therefore, we can generalize and say that any time a creature has this feature, you simply take their normal carrying/lifting/dragging/pushing capacity as determined for their size, and double it.
In the rare scenario where this feature gets applied to a 'Small'-sized creature, it would have no effect.