There is a way to breed parents' IVs onto their offspring, but we first need to figure out whether your Beldum and Ditto can produce your desired Pokemon. I've put your Beldum's stats into Serebii's IV Calculator and assuming your Beldum has no EVs and a neutral nature, your Beldum's HP IV is between 0-9 and your Attack IV is between 0-19. Both are extremely vague indicators, but they indicate that your Beldum has far from perfect IVs in those stats.
Realistically, the only thing you're able to do now is to continue hatching eggs until you get a Beldum with a good HP and/or Attack IV. Note, you don't need perfect IVs in both stats, but its preferred; more on that later. Also try searching for Ditto in the Pokemon Mansion and get a Ditto with a perfect HP and/or Attack IV. There needs to be a perfect HP and a perfect Attack IV somewhere between your Beldum and Ditto couple. With every Pokemon you hatch/encounter, be sure to use the IV Calculator I linked above. Fill out the other stuff I left out, such as your Pokemon's nature and overall potential (the latter indicated by the Pokemon Judge near the Battle Tower PC), as these will give you a more precise indication of your Pokemon's IVs.
Once you have gotten your two Pokemon, put them in the Daycare and wait patiently! The breeding mechanics work in that two IVs will come from one parent, and one IV will come from the other. I'm not sure how the probability works here, but I believe a higher probability results in having one perfect IV on one parent and the other IV on the other parent. That being said, the best probability is when both Pokemon have perfect HP and Attack IVs! That takes a bit of effort though, so do what you can. It will take a bit of hatching, but if you persevere, eventually you'll get your desired Beldum.
Hope I helped. :)
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