Reading between the lines of your post I will assume that you are operating SSB below 10 MHz, lower sideband (LSB), on a v6 uBiTx.
The issue that is reported to you is that your output signal is bleeding into the upper sideband (USB). This can be caused by the BFO not in alignment with the SSB filter. It can also be caused by overdriving the audio input on the rig.
The procedure that Ashhar Farhan outlines in the video post is the correct one for the alignment of the BFO. Just be careful to go more towards the 3 KHz red marker than the 500 Hz for the BFO adjustment. As Reed stated, it will sound a little tinny.
Monitoring your signal is the only way short of a spectrum analyzer (SA) to verify your output signal. To check your own signal, you might want to find a Web-based SDR site to monitor for yourself. There are a number of them around the work listed at
Find one in an area where you have received the bleed issue report if possible, otherwise one that can hear your transmission.
If you do want to go the SA route, I have been having good results recently with an RSP2 SDRPlay. They no longer make that model, however, the specifications of the RSP1a are better and list price is currently $109 US. The SA software is free and is now able to do all of the signal purity measurements that the prior releases could not. You will also need a directional tap. I made one from this article:
And a step attenuator like this one:
So far this is the lowest cost approach that I have found for a SA. The total cost including all parts, adapters, and cables should be less than $200 US, less if you shop around. There is a homebrew SA built with parts from eBay that I plan to try. I do not recommend an RTL-SDR dongle, the RF Explorer, nor the Analog Discover 2. I have tried all three and they have not produced results that are consistent or require multiple setups to do the harmonic tests. This is not the case that others have reported, so it may be that I do not have the correct setup for them.
Above are just suggestions, you are responsible for the signal purity of your radios.