Contrary to some of the other answers, I wouldn't start with removing high frequencies with EQ. I would instead start with removing low frequencies.
If the lav mics are cardioid, then they will emphasize low frequencies in a way that a typical outdoor location shotgun mic does not. Even omni lav mics can end up with some low frequency emphasis if they are pinned to the chest of the speaker. Removing low end also helps manage rustle and rumble that may get into lav mics.
The other big difference in the lav mic sound is what the mic doesn't pick up as well, which are the ambient sounds. For example, if there is a road or the ocean or a forest nearby, it will help to be able to hear (at a low level) the sounds typical for these environments.
Finally, as some other have suggested, reverb can help - but for outdoor scenes it really has to be the right reverb. A typical algorithmic reverb will not easily sound like a forest, hill, cliff, beach, roadway, city, etc. Instead, careful use of a convolution reverb (the kind that uses IRs) with the right IR can really make a difference. I have found and used in the past IRs taken in woods and other outdoor spaces that have some reflective surfaces (like the ground) and this kind of reverb can really make the sound more natural. This is assuming you can find the right IR and take the time to adjust the amount and processing of the reverb.
I know I said "finally" above, but I do want to circle back to reducing high frequencies. On a very dry day (clear skies, bright sun, cooler weather, no haze), high frequency attenuation can be audible at closer distances. If the on-camera speaker is within 3 meters/10 feet of the camera, it's not worth it decreasing the high frequencies. At 10 meters/30 feet at 50% relative humidity, you may see 3-6 dB of attenuation above 10 kHz. So only when a sound seems to be pretty far away does high frequency attenuation help with the illusion of distance. Think of a horn from far off or someone shouting from the other side of a sports field/pitch.
When a person is facing away from the camera, their head and body also block highs, so you could automate rolling off some highs when they are facing away and bringing them back when they turn towards the camera.
I do want to say that since it's a vlog, there may not be much expectation by viewers of a natural sound.