I suggest you to read the manual another time and use the “@” char 😛 which allow to di almost everything.
Compile this code twice :
`\documentclass{article}
\usepackage{chemfig}
\begin{document}
\chemfig{@a\lewis{2:,N}(-[:-20]H)(-[:-75,0.8]H)(-[:-160]H)-[@{b,1}2,,,,draw=none]H\rlap{${}^+$}}
\chemmove{\draw[-stealth,shorten <=5pt](a)--(b);}
\end{document}`
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