I would like to number the Affiliations of the Author's names in Arabic
If your objective is to use Arabic numerals instead of lowercase Latin letters as the footnote markers associated with the authors' affiliations, simply provide the option numafflabel to the \documentclass instruction:
\documentclass[preprint,12pt,numafflabel]{elsarticle}
Addendum, as suggested by @leandriis: The numafflabel option is present in version 3.2 of the elsarticle document class, but for some reason it is not documented in the package's user guide.
The package also provides the reversenotenum document class option, which (a) is documented and (b) purports to use arabic numerals for the author affiliations and alphabetic-letter footnote markers for "regular" footnotes, i.e., those in the body of the text. Unfortunately, the reversenotenum option doesn't seem to work correctly in version 3.2: The option does change the numbering style for affiliation-related footnote markers from alphabetic to arabic, but it does not change the footnote marker style for regular footnotes to alphabetic letters. :-(
A full MWE (minimum working example):

\documentclass[preprint,12pt,numafflabel]{elsarticle}
\begin{document}
\begin{frontmatter}
\title{My title}
\author[affiliation1,affiliation2]{Author1}
\author[affiliation3,affiliation5]{Author2}
\author[affiliation2]{Author3}
\author[affiliation3,affiliation4,affiliation6]{Author4}
\address[affiliation1]{Institute1}
\address[affiliation2]{Institute2}
\address[affiliation3]{Institute3}
\address[affiliation4]{Institute4}
\address[affiliation5]{Institute5}
\address[affiliation6]{Institute6}
\end{frontmatter}
\end{document}
reversenotenumallows to switch the nunbering style of author affiliations and author footnotes between arabic numbers and letters. – leandriis May 12 '19 at 06:52