The formula is LiHCO₃.
Since the compound contains a metal, it must be ionic. It must consist of M ions and HCO3 ions.
The formula for an HCO3 ion is HCO₃⁻, so the metal ion must be M⁺.
M must be an alkali metal; Li, Na, K, Rb, or Cs. All these form ions with a charge of +1.
Wikipedia states that all the alkali metals except Li can form compounds with oxidation number -1. I haven't been able to find examples of such compounds.
If we take Wikipedia at its word, the metal must be lithium.
The formula is then LiHCO₃.