Typing Unicode within Windows programs can differ from program to program and Word has a couple of alternatives.
Since you know the Unicode for the Devanagari Letter Vocalic L (ऌ), the easiest is to simply type 90c then immediately tap Alt+x. This should produce the ऌ character where 90c was typed.
The Word symbol library (Insert, Symbol, More Symbols) also has the ऌ character available within the Devanagari sub set.
hese symbols can be assigned to a hot-key or instituted into the AutoCorrect entries if used repetitively.
The term "(normal text)" in the Symbol dialog just means the font at the insertion point (usually the Default Paragraph Font). If you change the font of the paragraph (or style) to Mangal, then you will see the Devanagari character subset. Hrasva sound of ye and o also be similarly typed for sourashtri language.