Aligning unnumbered chapter title with numbered chapter titles in memoir TOC

Question

I am typesetting a thesis using the memoir class, and the chapters in the TOC are formatted like this

Abstract
1 Introduction

and I'd like them to be aligned like this:

  Abstract    
1 Introduction

Any suggestions on how to do this?

Answer 1

It would really have helped if you had given an MWE that showed what you have done. Given that we don't know that here is a possible MWE that at least guides you to solving your problem.

% memchaptocprob.tex SE 537676 Align (un)numbered chapter titles in the ToC

\documentclass{memoir}

\begin{document}
\frontmatter  % chapters are unnumbered
\tableofcontents
% set the indent to the space for chapter numbers
\addtocontents{toc}{\setlength{\cftchapterindent}{\cftchapternumwidth}}

\chapter{Abstract}
\mainmatter % chapters are numbered
% revert the chapter indents to the default
\addtocontents{toc}{\setlength{\cftchapterindent}{0em}}

\chapter{Main}
\end{document}

If you want a more automatic way of getting what you want please read the memoir.cls code, but I don't recommend this as you might end up tweaking the class internals