The specifications for the Lime Mini clearly state that the operational bandwidth is from 30 MHz to 3.7 GHz. So there is no direct solution to seeing signals below 30 MHz.
If you absolutely have to have a look at signals below 30 MHz I would suggest using an upconverter with the LO sourced from the TX channel.
You will also find that reading and understanding the ARRL Radio Handbook to be VERY helpful. You will find many solutions illustrating your delima. It’s a very easy problem and solution. However, your going to need to solder up a few components.
There is a lot to know, so be kind to yourself.
Most importantly, don’t be fooled by the relatively low price of the Lime Mini. 10 years ago you would have paid 10’s of thousands of dollars to have the same functionality. It is a very sophisticated device.