mik888em,
<pre>
<script>
let str = `===============
f fgyuf
с Scryptics
s Nartelis19
rhvrihvieg445gv54vuv
===============
gk qwerty gfhfg
с h5vvh5vh5vh5
s bj65v54gc4g
gdfgdsggrsgdg433
===============
dgf ffrffef
c c4ccf4cf4cf4fc4
s Ugniukas1
v4gv4v5g4g4vg5v4
===============
gk qwerty kfefdf
c vg545v4gv45gv5g4v5g4
s jb6jb6jb6j
g4g4vv4gv4gvg4
===============
gtth vdvfv gtggg
c vg4vg45v45gvg4545vgv45g
s v454vgv545v4gvg45
v4gg4vvg4g4vvg4vg45vg45vg4545vg
===============
fvdver 443342
c cffx2sx2xs2xs2
s xe332xd23f4v5gh5b6
445vgv45gv45gv45gv45g45vg
===============
`;
let save = 0, txt = 'gk qwerty'
str = str.split(/\n/).filter(a => {
if(save-- > 0) return true;
save = a.includes(txt) ? 2 : 0
});
document.write(str.join('\n'))
</script>
</pre>