How can Nyquist Frequency increase SNR?
I think you actually mean how can increasing the sampling rate (and by inference the nyquist rate) increase the resolution of an ADC.

I also think you meant SNR(dB) = 6.02 N + 1.76 rather than 6.02ENOB + 1.76.

Just going thru the errors in your question....

Dynamic range has also nothing to do with gain - it has everything to do with the bandwidth of your signal, the ADC sampling rate and the ADC bit-resolution. For instance, if the BW of your signal is 20 kHz the minimum sampling rate is 40kHz but, if you over sample by 4 (160 kHz) then you effectively increase the resolution of your ADC by 1 bit. Oversample by 4 times again and you retrieve another bit of resolution. This is basically the theory behind sigma delta ADCs but applies equally to any ADC.

I'd urge you to read this document by analog Devices entitled "Understand SINAD, ENOB, SNR, THD, THD + N, and SFDR so You Don't Get Lost in the Noise Floor".