This study will include participants with relapsed/refractory (R/R) Multiple Myeloma (MM). MM is a type of cancer of the blood. This study will also include participants with relapsed/refractory (R/R) Diffuse Large B-Cell Lymphoma (DLBCL). DLBCL is also a type of cancer of the blood. They are referred to as ‘relapsed’ when the disease has come back after treatment and ‘refractory’ when treatment no longer works. The study has 2 main parts, called phase 1 and phase 1b. The main objective of both parts will be to evaluate the safety and tolerability of the study drug, called EZM0414. The main objective of phase 1b will also be to determine the effectiveness of EZM0414. During phase 1 six dose levels will be tested. Participants will receive study drug at the assigned dose level every 28 days. During phase 1b participants will receive study drug at the maximum tolerated dose in 28-day cycles.