regular 501s may shrink but because the jeans is sanforized the difference will be too small - ~0.5-1inch
we need unsanforized denim / 501 shrink-to-fit jeans

most extreme way==wash it with hot water and use machine dryer, do this many many times until you get the satisfied result but i warn you the dye probably fade out later and texture of the fabric will ruins and not durable anymore to handle everyday abuse

most fabrics are really really being sanforized that shrink it would be too much hassle with near to zero effect, i would better just send it to tailor shop to have it downsize 2-3inch smaller

my 501 only shrunk ~0.5inch in teh waist after 3hot washes